Reflection type liquid crystal display device with a passivation layer directly on the pad electrode

ABSTRACT

Disclosed are a reflection type LCD and method of manufacturing the same. A wiring layer having a first and second metal layer ( 102, 104 ) is formed on a substrate ( 100 ) including a display region (D) and a pad region (P). Upon the substrate ( 100 ) and the wiring layer is formed a first passivation layer ( 155 ), and contacts with a wiring terminal ( 115 ) and the first metal layer ( 102 ). A second passivation layer ( 180 ) is formed on the substrate except the pad region (P). The pad contact hole ( 160 ) extends to a position under the second passivation layer ( 180 ). The second passivation layer ( 180 ) covers a region in the pad contact hole ( 160 ) where the step coverage of the pad electrode ( 170 ) is poor, thereby preventing a battery effect.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device and amethod of manufacturing the same, and more particularly to a reflectiontype liquid crystal display device and a method of manufacturing thesame in which a battery effect can be prevented when a pad electrodeconsisting of a transparent conductive layer is used.

BACKGROUND ART

In the information society of these days, electronic display devices aremore important as information transmission media and various electronicdisplay devices are widely applied for industrial apparatus or homeappliances. Such electronic display devices are being continuouslyimproved to have new appropriate functions for various demands of theinformation society.

In general, electronic display devices display and transmit variouspieces of information to users who utilize such information. That is,the electronic display devices convert electric information signalsoutputted from electronic apparatus into light information signalsrecognized by users through their eyes.

In the electronic display devices dividing into an emissive displaydevice and a non-emissive display device, the emissive display devicedisplays light information signals through a light emission phenomenathereof and the non-emissive display device displays the lightinformation signals through a reflection, a scattering or aninterference thereof. The emissive display device includes a cathode raytube (CRT), a plasma display panel (PDP), a light emitting diode (LED)and an electroluminescent display (ELD). The emissive display device iscalled as an active display device. Also, the non-emissive displaydevice, called as a passive display device, includes a liquid crystaldisplay (LCD), an electrochemical display (ECD) and an electrophoreticimage display (EPID).

The CRT has been used for a television receiver or a monitor of acomputer as the display device for a long time since it has a highquality and a low manufacturing cost. The CRT, however, has somedisadvantages such as a heavy weight, a large volume and high powerdissipation.

Recently, the demand for a new electronic display devices is greatlyincreased such as a flat panel display device having excellentcharacteristics that thin thickness, light weight, low driving voltageand low power consumption. Such flat panel display devices can bemanufactured according to the rapidly improved semiconductor technology.

In the flat panel devices, a liquid crystal display (LCD) device hasbeen widely utilized for various electronic devices because the LCDdevice has thin thickness, low power dissipation and high displayquality approximately identical to those of the CRT. Also, the LCDdevice can be operated under a low driving voltage and can be easilymanufactured so that the LCD device is widely used for variouselectronic apparatuses.

The LCD devices are generally divided into a transmission type LCDdevice, a reflection type LCD device and a reflection-transmission typeLCD device. The transmission type LCD device displays information byusing a light source such as a backlight and the reflection type LCDdevice displays information by using an external natural light. Thereflection-transmission type LCD device operates in a transmission modefor displaying an image using a built-in light source of the LCD devicein a room or in a dark place where an external light source does notexist, and operates in a reflection mode for displaying the image byreflecting an incident light in the outside.

At present, a thin film transistor-liquid crystal display device(TFT-LCD) is predominantly used. The thin film transistor-liquid crystaldisplay device has a structure that two substrates respectively havingelectrodes are provided and a thin film transistor (TFT) for switching avoltage applied to the electrodes is generally formed in a pixel regionof one of the substrates. The thin film transistor-liquid crystaldisplay devices are divided into an amorphous typed TFT-LCD and apolycrystalline typed TFT-LCD.

FIGS. 1A and 1B are cross-sectional views showing a reflection typeliquid crystal display device according to a conventional method. InFIGS. 1A and 1B, the reflection type liquid crystal display device is anamorphous silicon TFT-LCD having a bottom-gate structure. Referring toFIG. 1B, a reference symbol P shows a pad region; a reference symbol Dindicates a display region; and a reference symbol B shows a boundaryregion located between the pad region and the display region.

Referring to FIGS. 1A and 1B, after sequentially depositing a chrome(Cr) layer 11 and an aluminum-neodymium (AlNd) layer 12 on a substrate10 composed of an insulating material such as glass, quartz or sapphire,these layers are patterned by a photolithography process to form a gatewiring. The gate wiring includes a gate line 13 prolonged in a firstdirection, a gate electrode 12 of a thin film transistor branched fromthe gate line 13 and a gate terminal 15 connected to the end of the gateline 13.

A gate insulation layer 16 composed of silicon nitride is formed on thesubstrate 10 on which the gate wiring is formed, and then, an amorphoussilicon layer and an n⁺ doped amorphous silicon layer are successivelydeposited on the gate insulation layer 16. Subsequently, the amorphoussilicon layer and the n⁺ doped amorphous silicon layer are patterned viaa photolithography process to form an active pattern 17 and an ohmiccontact pattern 18. Thus, the active pattern 17 is composed of amorphoussilicon and the ohmic contact pattern 18 is made of n⁺ doped amorphoussilicon.

After depositing a second metal layer, e.g., chrome (Cr) layer, on theohmic contact pattern 18 and the gate insulation layer 16, the secondmetal layer is patterned through a photolithography process to form adata wiring. The data wiring includes a data line 19 prolonged in asecond direction perpendicular to the first direction, source/drainelectrodes 20 and 21 branched from the data line 19 and a data terminal22 connected to the end of the data line 19.

Then, a portion of the ohmic contact pattern 18 exposed between thesource electrode 20 and the drain electrode 22 is dry-etched away tocomplete the thin film transistor.

After forming an inorganic passivation layer 24 comprised of siliconnitride on the data wiring and the gate insulation layer 16, a portionof the inorganic passivation layer 24 over the drain electrode 21 isremoved. At the same time, there are formed a first pad contact hole 25for exposing the gate terminal 15 and a second pad contact hole 26 forexposing the data terminal 22.

After forming an organic passivation layer 26 on the entire surface ofthe resultant structure, a portion the organic passivation layer 26 overthe drain electrode 22 and the pad regions is removed by exposure anddevelopment processes to form a contact hole 29 exposing the drainelectrode 22. At the same time, numerous grooves 30 for scattering alight are formed at the surface of the organic passivation layer 26.

After depositing a reflective layer composed of metal having highreflectivity such as aluminum-neodymium (AlNd) on the entire surface ofthe resultant structure, the reflective layer is patterned by aphotolithography process to form a reflective electrode 32 connected tothe drain electrode 21 through the contact hole 29. At the same time,there are formed a gate pad electrode 33 connected to the gate terminal15 through the first pad contact hole 25 for applying a scanning voltageto the gate electrode 14 and a data pad electrode 34 connected to thedata terminal 22 through the second pad contact hole 26 for applying asignal voltage to the source electrode 20.

According to the above conventional reflection type liquid crystaldisplay device, the pad electrodes 33 and 34 are simultaneously formedwhen forming the reflective electrode 32 composed of aluminum alloy suchas aluminum-neodymium (AlNd). Thus, during a subsequent chip on glass(COG) bonding process by which integrated circuits are directly mountedon the substrate of the LCD panel, COG (chip on glass) block defects maybe caused due to aluminum corrosion. Therefore, there is suggested amethod where a pad electrode is formed of an indium-tin-oxide (ITO) usedas a transparent electrode.

FIG. 2 is a cross-sectional view of a reflection type liquid crystaldisplay device manufactured by another conventional method. Here, areference symbol P shows a pad region; a reference symbol D indicated adisplay region; and a reference symbol B shows a boundary region locatedbetween the pad region and the display region.

Referring to FIG. 2, after sequentially depositing a chrome (Cr) layer51 and an aluminum-neodymium (AlNd) layer 52 on a substrate 50 composedof an insulating material such as glass, these layers are patterned by aphotolithography process to form a gate wiring. The gate wiring includesa gate line 53 prolonged in a first direction, a gate electrode (notshown) branched from the gate line 53 and a gate terminal 54 connectedto the end of the gate line 53.

A gate insulation layer 55 composed of silicon nitride is formed on thesubstrate 50 on which the gate wiring is formed. Then, an active pattern(not shown) composed of amorphous silicon and an ohmic contact pattern(not shown) composed of n⁺ doped amorphous silicon are successivelyformed on the gate insulation layer 55.

After depositing a second metal layer, e.g., a chrome (Cr) layer, on theohmic contact pattern and the gate insulation layer 55, the second metallayer is patterned by a photolithography process to form a data wiring.The data wiring includes a data line 56 prolonged in a second directionperpendicular to the first direction, source/drain electrodes (notshown) branched from the data line 56 and a data terminal 58 connectedto the end of the data line 56. Successively, a portion of the ohmiccontact pattern exposed between the source electrode and the drainelectrode is dry-etched away.

After forming an inorganic passivation layer 60 on the data wiring andthe gate insulation layer 55, a portion of the inorganic passivationlayer 60 over the drain electrode is removed by a photolithographyprocess. At the same time, there are formed a first pad contact hole 61exposing the gate terminal 54 and a second pad contact hole 62 exposingthe data terminal 58. In general, ITO and Al cannot be in contact witheach other due to a galvanic corrosion. Thus, during the formation ofthe pad contact holes 61 and 62, the entire exposed AlNd layer 52 of thegate terminal 54 is etched away using a wet etching process. By doingso, an ITO pad electrode being formed in a subsequent process is incontact with the Cr layer 51 of the gate terminal 54. However, when theAlNd layer 52 exposed through the first pad contact hole 61 is etchedaway, the side of the AlNd layer 52 is etched away due to the isotropicproperty of wet etching to thereby generate an undercut 64.

Next, an ITO layer is deposited on the pad contact holes 61 and 62 andthe inorganic passivation layer 60 and then, patterned by aphotolithography process to thereby form a gate pad electrode 65 and adata pad electrode 66. The gate pad electrode 65 is connected to thegate terminal 54 through the first pad contact hole 61 and the data padelectrode 66 is connected to the data terminal 58 through the second padcontact hole 62. At this time, step coverage of the date pad electrode65 becomes poor on a stepped portion in the first pad contact hole 61,i.e., the undercut region 64.

After forming an organic passivation layer 68 on the pad electrodes 65and 66 and the inorganic passivation layer 60, the organic passivationlayer 68 is patterned by an exposure process and a development processto thereby form a contact hole (not shown) for exposing the drainelectrode. At the same time, numerous grooves 69 are formed in thesurface of the organic passivation layer over the display region.

After sequentially depositing a barrier metal layer 70 composed ofmolybdenum-tungsten (MoW) and a reflective layer composed ofaluminum-neodymium (AlNd) on the contact hole and the organicpassivation layer 68, the reflective layer and the barrier metal layer70 are patterned by a photolithography process to thereby form areflective electrode 72 connected to the drain electrode through thecontact hole.

According to the above conventional method, in order to prevent thegalvanic corrosion caused between ITO and Al, the entire AlNd layer 52of the gate terminal 54 is etched away using a wet etching process whenthe pad contact holes 61 and 62 are formed. Thus, the undercut 64 isgenerated in the AlNd layer 52.

Further, two photolithography processes for forming the organicpassivation layer 68 and the reflective electrode 72 are carried outafter the pad electrodes 65 and 66 are formed. Moreover, in order toimprove the pixel contact characteristics, an etching process using analuminum etchant is added before forming the reflective electrode 72.Accordingly, during performing the above processes, chemicals such as adevelop solution or an etchant penetrate through the stepped portion(portion “A” in FIG. 2) in the first pad contact hole 61 to therebycorrode the AlNd layer 52. In addition, such chemicals serve as anelectrolyte to cause a battery effect between Al and ITO, therebygenerating a lifting of the gate pad electrode 61.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the aforementioned problem,and accordingly, it is an object of the present invention to provide areflection type liquid crystal display device in which a battery effectcan be prevented when a pad electrode consisting of a transparentconductive layer is used.

It is another object of the present invention to provide a method ofmanufacturing a reflection type liquid crystal display device in which abattery effect can be prevented when a pad electrode consisting of atransparent conductive layer is used.

To achieve the object of the present invention, there is provided areflection type liquid crystal display device comprising a substrateincluding a display region and a pad region located outside the displayregion, a wiring layer formed on the substrate, the wiring layer beingcomprised of a first metal layer and a second metal layer stacked on thefirst metal layer and including a wiring layer terminal located on thepad region; a first passivation layer formed on the substrate and thewiring layer and having a pad contact hole for exposing the wiring layerterminal and the first metal layer of a portion of the wiring layerconnected to the wiring layer terminal; a pad electrode continuouslyformed on the sidewall and bottom of the pad contact hole and on aportion of the first passivation layer, the pad electrode beingcomprised of a transparent conductive layer and making contact with thewiring terminal and the first metal layer of a portion of the wiringlayer connected to the wiring layer terminal; a second passivation layerformed on the substrate except the pad region; and a reflectiveelectrode formed on the second passivation layer of the display region,wherein the pad contact hole is extended to a position under the secondpassivation layer located on a boundary region between the displayregion and the pad region.

Further, to achieve the above object of the present invention, there isprovided a reflection type liquid crystal display device comprising asubstrate including a display region and a pad region located outsidethe display region; a gate wiring formed on the substrate, the gatewiring being comprised of a first metal layer and a second metal layerstacked on the first metal layer and including a gate line prolonged ina first direction and a gate terminal formed on the pad region andconnected to the end of the gate line; a gate insulating layer formed onthe gate wiring and the substrate; a data wiring formed on the gateinsulating layer, the data wiring including a data line prolonged in asecond direction perpendicular to the first direction and a dataterminal formed on the pad region so as to be connected to the end ofthe data line; a first passivation layer formed on the data wiring andthe gate insulating layer, the first passivation layer having a firstpad contact hole formed through the gate insulating layer to expose thegate terminal and the first metal layer that is a portion of the gateline connected to the gate terminal; a gate pad electrode continuouslyformed on the sidewall and bottom of the first pad contact hole and on aportion of the first passivation layer, the gate pad electrodeconsisting of a transparent conductive layer and being in contact withthe gate terminal and the first metal layer of a portion of the gateline connected to the gate wiring; a second passivation layer formed onthe substrate except the pad region; and a reflective electrode formedon the second passivation layer of the display region, wherein the firstpad contact hole is extended to a position under the second passivationlayer located on a boundary region between the display region and thepad region.

To achieve another object of the present invention, there is provided amethod of manufacturing a reflection type liquid crystal display devicecomprising the steps of forming a wiring layer on a substrate includinga display region and a pad region located outside the display region,the wiring layer being comprised of a first metal layer and a secondmetal layer stacked on the first metal layer and including a wiringlayer terminal located on the pad region; forming a first passivationlayer on the substrate and the wiring layer, the first passivation layerhaving a pad contact hole for exposing the wiring layer terminal and thefirst metal layer of a portion of the wiring layer connected to thewiring layer terminal; continuously forming a pad electrode comprised ofa transparent conductive layer on the sidewall and bottom of the padcontact hole and on a portion of the first passivation layer, the padelectrode making contact with the wiring terminal and the first metallayer of a portion of the wiring layer connected to the wiring layerterminal; forming a second passivation layer on the substrate except thepad region; and forming a reflective electrode on the second passivationlayer in the display region.

Further, to achieve anther object of the present invention, there isprovided a method of manufacturing a reflection type liquid crystaldisplay device comprising the steps of forming a gate wiring on asubstrate including a display region and a pad region located outsidethe display region, the gate wiring being comprised of a first metallayer and a second metal layer stacked on the first metal layer andincluding a gate line prolonged in a first direction and a gate terminalformed on the pad region and connected to the end of the gate line;forming a gate insulating layer on the gate wiring and the substrate;forming a data wiring on the gate insulating layer, the data wiringincluding a data line prolonged in a second direction perpendicular tothe first direction and a data terminal formed on the pad region so asto be connected to the end of the data line; forming a first passivationlayer on the data wiring and the gate insulating layer, the firstpassivation layer having a first pad contact hole formed through thegate insulating layer to expose the gate terminal and the first metallayer of a portion of the gate line connected to the gate terminal;continuously forming a gate pad electrode comprised of a transparentconductive layer on the sidewall and bottom of the first pad contacthole and on a portion of the first passivation layer, the gate padelectrode being in contact with the gate terminal and the first metallayer of a portion of the gate line connected to the gate wiring;forming a second passivation layer on the substrate except the padregion; and forming a reflective electrode on the second passivationlayer in the display region.

According to the present invention, the pad electrode comprised of thetransparent conductive layer is formed after an opening region of thefirst passivation layer, i.e., the pad contact hole, is formed so as tobe extended to a position under the second passivation layer located onthe boundary region between the display region and the pad region. Thus,the second passivation layer covers a portion where step coverage of thepad electrode is poor due to a stepped portion of the opening region,i.e., an undercut of the second metal layer. Therefore, it can beprevented chemicals from penetrating through the stepped portion of theopening region to cause the battery effect between the pad electrode andthe second metal layer of the wiring layer, thereby preventing a liftingof the pad electrode and a corrosion of the second metal layer.

Further, the first metal layer of the wiring layer exposed through thepad contact hole is covered with the pad electrode to the boundaryregion located between the display region and the pad region. Thus, whenthe first metal layer of the wiring layer terminal is short-circuited ona predetermined region, a redundancy can be formed by the pad electrodecovering the first metal layer that is not short-circuited.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects and advantages of the present invention willbecome readily apparent by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings wherein:

FIGS. 1A and 1B are cross-sectional views showing a reflection typeliquid crystal display device manufactured according to one conventionalmethod;

FIG. 2 is a cross-sectional view illustrating a reflection type liquidcrystal display device manufactured by another conventional method;

FIG. 3 is a plan view showing a reflection type liquid crystal displaydevice according to a present invention;

FIGS. 4A and 4B are cross-sectional views showing the reflection typeliquid crystal display device, taken along lines E-E′ and F-F′ in FIG.3; and

FIGS. 5A to 9B are cross-sectional views illustrating a method ofmanufacturing the reflection type liquid crystal display device shown inFIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a reflection type liquid crystal display device and amethod of manufacturing the reflection type liquid crystal displaydevice according to the preferred embodiments of the present inventionwill be described in detail with reference to the accompanying drawings.

FIG. 3 is a plan view showing a reflection type liquid crystal displaydevice according to the present invention. FIGS. 4A and 4B arecross-sectional views of the reflection type liquid crystal displaydevice, taken along lines E-E′ and F-F′ in FIG. 3, respectively. Thereflection type liquid crystal display device includes an amorphoussilicon thin film transistor having a bottom-gate structure. Here, areference symbol P shows a pad region; a reference symbol D indicated adisplay region; and a reference symbol B shows a boundary region locatedbetween the pad region and the display region. Here, the pad region P isformed outside the display region D so as to surround the display regionD.

Referring to FIGS. 3, 4A and 4B, a gate wiring is formed on a substrate100 made of an insulating material such as glass, quartz or sapphire.The gate wiring is comprised of double metal layers including a firstmetal layer 102 consisting of chrome (Cr), molybdenum (Mo), tantalum(Ta) or a titanium (Ti) and a second metal layer 104 consisting ofaluminum alloy such as aluminum (Al) or aluminum-neodymium (AlNd)stacked on the first metal layer 102. The gate wiring includes a gateline 105 prolonged in a first direction (i.e., a horizontal direction),a gate electrode 110 of a thin film transistor 195 branched from thegate line 105, and a gate terminal 115 formed on the pad region (P) andconnected to the end of the gate line 115.

A gate insulation layer 120 is formed on the gate wiring and thesubstrate 100. The gate insulation layer 120 is comprised of aninorganic material such as silicon nitride. An active pattern 125 and anohmic contact pattern 130 are successively formed on the gate insulationlayer 120 where the gate electrode 110 is located. The active pattern125 is comprised of amorphous silicon and the ohmic contact pattern 130is comprised of n⁺ doped amorphous silicon.

Further, a data wiring made of a single metal layer such as chrome (Cr)is formed on the gate insulation layer 120 and the ohmic contact pattern130. The data wiring includes a data line 135 prolonged in a seconddirection (i.e., a vertical direction) perpendicular to the firstdirection, first and second electrodes 140 and 145, and a data terminal150 formed on the pad region (P) so as to be connected to the end of thedata line 135. The first electrode 140 (source electrode or drainelectrode) is branched from the data line 135 and overlapped with afirst region of the active pattern 125. The second electrode 145 (drainelectrode or source electrode) is overlapped with a second region of theactive pattern 125 opposed to the first region. Hereinafter, the firstelectrode 140 is called as the source electrode and the second electrode145 is called as the drain electrode.

Upon the data wiring and the gate insulating layer 120, there is formeda first passivation layer 155 having a first pad contact hole 160exposing the gate terminal 115 and a portion of the gate line 105connected to the gate terminal 115 and a second pad contact hole 175exposing the data terminal 150. Preferably, the first passivation layer155 is comprised of an inorganic material such as silicon nitride. Thefirst pad contact hole 160 is formed through the first passivation layer155 and gate insulating layer 120 to thereby expose the gate terminal115 and the first metal layer 102 that is a portion of the gate line 105connected to the gate terminal 115.

A gate pad electrode 170 comprised of a transparent conductive layer,preferably ITO, is formed continuously on the sidewall and bottom of thefirst pad contact hole 160 and on a portion of the first passivationlayer 155. Through the first pad contact hole 160, the gate padelectrode 170 makes contact with the gate terminal 115 and the firstmetal layer 102 that is a portion of the gate line 105 connected to thegate terminal 115 so as to apply a scanning voltage to the gateelectrode 110. Further, a data pad electrode 175 made from the samelayer as in the gate pad electrode 170 makes contact with the dataterminal 150 through the second pad contact hole 165 so as to apply asignal voltage to the source electrode 140.

A second passivation layer 180 comprised of an organic material such asphotosensitive acrylic resin is formed on the first passivation layer155. In the display region (D) where pixels are formed to display animage, numerous grooves 30 for scattering a light to enhance thereflectivity are formed at the surface of the second passivation layer180. The first passivation layer 155 comprised of an inorganic materialis provided in order to maintain the reliability of the transistor andpads and to enhance the adhesion of a COG bonding. To achieve suchpurpose, the second passivation layer 180 comprised of an organicmaterial is formed only on the region except the pad region (P).

On the second passivation layer 180, there is formed a reflectiveelectrode 185 connected to the drain electrode 145 via a contact hole185 formed through a first passivation layer 155 and the secondpassivation layer 180. The reflective electrode 185 severs as areflector for reflecting a light being irradiated upon the substrate 100from the outside and simultaneously, serves as a pixel electrode forreceiving an image signal from the thin film transistors 195, which areformed on the respective pixel region of the substrate 100, to generatean electric field with an electrode (not shown) of an upper substrate(i.e., color filter substrate). The reflective electrode 185 is formedin the pixel region confined by the gate line 105 and the data line 135.Further, in order to secure a high aperture ratio, the edges of thereflective electrode 185 are overlapped with the gate line 105 and thedata line 135. Though not shown in the figure, a barrier metal layer maybe formed under the reflective electrode 185. The barrier metal layer iscomprised of a metal having an etching rate similar to that of thereflective electrode 185 with respect to a predetermined etchant, and ispreferably comprised of molybdenum-tungsten (MoW).

According to the reflection type liquid crystal display device of thepresent invention, an opening region of the first passivation layer 155,i.e., the first pad contact hole 160 is formed so as to be extended tobe formed under the second passivation layer 155 located on the boundaryregion (B) between the display region (D) and the pad region (P). As aresult, during subsequent processes after forming the pad electrodes 170and 175, it can be prevented chemicals from penetrating through a regionwhere step coverage of the gate pad electrode 170 is poor due to astepped portion in the first pad contact hole 160 (i.e., an undercut 162of the second metal layer 104), thereby preventing a battery effectcaused between the gate pad electrode 170 and the second metal layer104. Therefore, no defect such as a lifting of the gate pad electrode175 and a corrosion of the second metal layer 104 is generated.

Further, according to the reflection type liquid crystal display deviceof the present invention, the first metal layer 102 exposed through thefirst pad contact hole 160 is covered with the gate pad electrode 170 tothe boundary region (B). Therefore, when chemicals penetrate throughpinholes in ITO layer constituting the gate pad electrode 170 toshort-circuit the first metal layer 102 of the gate wiring, a redundancycan be formed of the gate pad electrode 170 covering the first metallayer 102 that is not short-circuited.

FIGS. 5A to 9B are cross-sectional views illustrating a method ofmanufacturing the reflection type liquid crystal display device shown inFIG. 4. Here, each of figures “a” are cross-sectional views taken alonga line E-E′ in FIG. 3, while each of figures “b” taken along a line F-F′in FIG. 3. A reference symbol P shows a pad region; a reference symbol Dindicates a display region; and a reference symbol B shows a boundaryregion located between the display region and the pad region.

Referring to FIGS. 5A and 5B, after sequentially depositing a firstmetal layer 102 and a second metal layer 104 on an insulating substrate100 comprised of glass, quartz or ceramic, these layers 104 and 102 arepatterned by a photolithography process using a first mask to form agate wiring. Preferably, the first metal layer 102 is comprised ofchrome (Cr) having a thickness of about 500 Å and the second metal layer104 is comprised of aluminum-neodymium (AlNd) having a thickness ofabout 2500 Å. The gate wiring includes a gate line 105 prolonged in afirst direction, a gate electrode 110 of a thin film transistor branchedfrom the gate line 105, and a gate terminal 115 connected to the end ofthe gate line 115.

Referring FIGS. 6A and 6B, an inorganic material, e.g., silicon nitride,is deposited to a thickness of about 4500 Å by a plasma-enhancedchemical vapor deposition (PECVD) method on the substrate 100 on whichthe gate wiring is formed, thereby forming a gate insulating layer 120.

An active layer, e.g., an amorphous silicon layer, is deposited to athickness of about 2000 Å by the PECVD method on the gate insulationlayer 120, and then, an ohmic contact layer, e.g., an n⁺ doped amorphoussilicon layer, is deposited to a thickness of about 500 Å by the PECVDmethod on the active layer. Here, the active layer and the ohmic contactlayer are in-situ deposited in the same chamber of the PECVD equipment.Next, the active layer and the ohmic contact layers are patterned by aphotolithography process using a second mask to form an active pattern125 and an ohmic contact pattern 130. The active pattern 125 remains onthe gate insulation layer 120 where the gate electrode 110 is located.

Then, after depositing a metal layer such as chrome (Cr) a thickness ofabout 1500 to about 4000 Å on the ohmic contact pattern 130 and the gateinsulation layer 120, the metal layer is patterned by a photolithographyprocess using a third mask to form a data wiring. The data wiringincludes a data line 135 perpendicular to the gate line 105,source/drain electrodes 140 and 145 branched from the data line 135, anda data terminal 150 connected to the end of the data line 135.

Subsequently, the ohmic contact pattern 130 exposed between the sourceelectrode 140 and the drain electrode 145 is removed by a reactive ionetching (RIE) method, thereby forming the thin film transistor 195 onthe display region (D). At that time, the gate insulation layer 120 isinterposed between the gate line 105 and the data line 135, therebypreventing the gate line 105 and the data line 135 from makingelectrical contact with each other.

In the present embodiment, the active pattern 125, the ohmic contactpattern 130 and the data wiring are formed using two masks. The presentinventors, however, invented and filed a method for forming an activepattern, an ohmic contact pattern and a data wiring using one mask asKorean Patent Application No. 1998-49710, thereby reducing the number ofmasks for manufacturing a thin film transistor-liquid crystal displaydevice having the bottom-gate structure. The method of manufacturingsuch thin film transistor-liquid crystal display device will bedescribed as follows using the same reference numerals concerningelements identical to the present embodiment.

At first, an active layer, an ohmic contact layer and a metal layer aresuccessively deposited on a gate insulation layer 120. After aphotoresist layer is coated on the metal layer, the photoresist layer ispatterned by exposure and developing processes to form a photoresistpattern (not shown) including a first portion, a second portion, and athird portion. The first portion has a first thickness and locates on achannel region of the thin film transistor. The second portion has asecond thickness thicker than that of the first portion and locates on aregion where a data wiring will be formed. The third portion is a regionwhere no photoresist layer remains.

Then, the metal layer, ohmic contact layer and active layer under thethird portion, the metal layer under the first portion, and a partialthick of the second portion are etched away to simultaneously form thedata wiring composed of the metal layer, the ohmic contact pattern 130comprised of the n⁺ amorphous silicon layer and the active pattern 125comprised of amorphous silicon layer. Next, the remaining thephotoresist patterns is removed. By doing so, the active pattern 125,the ohmic contact pattern 130 and the data wiring are formed at the sametime using one mask.

Referring to FIGS. 7A and 7B, an inorganic material, e.g., siliconnitride, is deposited to a thickness of about 2000 Å on the entiresurface of the substrate 100 on which the thin film transistor 195 isformed, thereby forming a first passivation layer. 155. The firstpassivation layer 155 assures reliabilities of the thin film transistorand the pads, and enhances the adhesion of integrated circuits during asubsequent COG bonding.

Next, through a photolithography process using a fourth mask, the firstpassivation layer 155 and the gate insulating layer 120 are etched awayto form a first contact hole 156 exposing the drain electrode 145. Atthe same time, there are formed a first pad contact hole 160 exposingthe gate terminal 115 and a portion of the gate line 105 connected tothe gate terminal 115, and a second pad contact hole 175 exposing aportion of the data terminal 150. The first pad contact hole 160 isextended to the boundary region (B) located between the pad region (P)and the display region (D), while the second pad contact hole 165 isformed only on the pad region (P).

At this time, since the gate terminal 155 exposed through the first padcontact hole 160 is the second metal layer 104 comprised ofaluminum-neodymium (AlNd), the entire exposed second metal layer 104 isetched away by a wet etching process using an aluminum etchant in orderto prevent the aluminum layer from making direct contact with an ITO padelectrode that will be formed in a subsequent process. As a result, thegate terminal 115 and the first metal layer 104 that is a portion of thegate line 105 connected with the gate terminal 115 are exposed throughthe first pad contact hole 160. No galvanic corrosion is generatedbetween the first metal layer 102 and the ITO pad electrode because thefirst metal layer 102 is comprised of chrome (Cr). When the second metallayer 104 comprised of aluminum-neodymium (AlNd) exposed by the firstpad contact hole 106 is etched as described above, the side wall of thesecond metal layer 104 is etched due to the isotropic characteristic ofthe wet etching method, thereby forming an undercut 162.

Referring to FIGS. 8A and 8B, a transparent conductive layer, preferablyITO layer, is deposited on the pad contact holes 160 and 165 and thefirst passivation layer 155, and then, patterned by a photolithographyprocess using a fifth mask. By doing so, there is formed a gate padelectrode 170 being in contact with the gate terminal 115 and the firstmetal layer 102 of a portion of the gate line 105 connected to the gateterminal 115 through the first pad contact hole 160. At the same time,there is formed a data pads electrode 175 making contact with the dataterminal 150 through the second pad contact hole 165.

In order to complete cover the first metal layer 102 exposed the firstpad contact hole 160, the gate pad electrode 170 is formed so as toextend to the boundary region (B) between the pad region (P) and thedisplay region (D). Accordingly, though chemicals penetrate throughpinholes in the ITO layer constituting the gate pad electrode 170 toshort-circuit the first metal layer 102, a redundancy can be formed bythe gate pad electrode 170 covering the first metal layer 102 that isnot short-circuited.

Referring to FIGS. 9A and 9B, an organic material having a lowdielectric constant, e.g., a photosensitive acrylic resin, is coated toa thickness more than 2 μm on the gate pad electrode 170, the data padelectrode 175 and the first passivation layer 155, thereby forming asecond passivation layer 180. Because the second passivation layer 180restrains a parasitic capacitance that is generated between the datawiring and a pixel electrode, the pixel electrode, i.e., a reflectiveelectrode, is formed so as to be overlapped with the gate line 105 anddata line 135, thereby accomplishing the thin film transistor-liquidcrystal display device having a high aperture ratio.

After a sixth mask having a pattern corresponding to a contact hole 185is positioned over the second passivation layer 180 in order to form thecontact hole 185 through the second passivation layer 180, a portion ofthe second passivation layer 180 over the drain electrode 145 and aportion of the second passivation layer 180 over the pad region (P) areprimarily exposed by a full exposure process. Next, a seventh mask forforming micro lenses is positioned over the second passivation layer180. A portion of the second passivation layer 180 over the displayregion (D) besides the contact hole 185 is secondarily exposed via alens exposure process. Subsequently, a develop process is carried outusing a solution including tetramethyl-ammonium hydroxide (TMAH) tothereby form the contact hole 185 and numerous grooves 182. The contacthole 185 extends from the first contact hole 156 to thereby expose thedrain electrode 145. At this case, the second passivation layer 180 overthe pad region (P) is removed.

Then, after performing a curing process at a temperature of about 130 to230° C. for about 100 minutes in order to reflow and to harden thesecond passivation layer 180, an entire-etching process using analuminum etchant is carried out for about a few minutes in order toenhance the pixel contact characteristics.

Next, a metal layer (not shown) having an etching rate similar to thatof a reflective layer constituting the reflective electrode with respectto an etchant for etching the reflective layer, e.g., amolybdenum-tungsten (MoW), is deposited to a thickness of about 500 Å onthe entire surface of the resultant structure, thereby forming a barriermetal layer (not shown). The reflective layer having a high reflectivitysuch as aluminum-neodymium (AlNd) or silver (Ag) is deposited to athickness of about 1500 Å on the barrier metal layer. Next, thereflective layer and the barrier metal layer are patterned through aphotolithography process using an eighth mask to thereby form thereflective electrode (reference numeral 190 in FIG. 4A). The reflectiveelectrode 190 serves as a reflector and a pixel electrode, and isconnected to the drain electrode 145 of the thin film transistor.

According to the present invention as described above, the pad electrodeconsisting of the transparent conductive layer is formed after anopening region of the first passivation layer, i.e., the pad contacthole, is formed so as to be extended to a position under the secondpassivation layer located on the boundary region between the displayregion and the pad region. By doing so, the second passivation layercovers a portion where the step coverage of the pad electrode is poordue to a stepped portion of the opening region, i.e., an undercut of thesecond metal layer. Therefore, it can be prevented chemicals frompenetrating through the stepped portion of the opening region to cause abattery effect between the pad electrode and the second metal layer ofthe wiring layer, thereby preventing a lifting of the pad electrode anda corrosion of the second metal layer.

Further, the first metal layer of the wiring layer exposed through thepad contact hole is covered with the pad electrode to the boundaryregion located between the display region and the pad region. Thus, whenthe first metal layer of the wiring layer terminal is short-circuited ona predetermined region, a redundancy can be formed by the pad electrodecovering the first metal layer that is not short-circuited.

Although the preferred embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these preferred embodiments but various changes andmodifications can be made by one skilled in the art within the spiritand scope of the present invention as hereinafter claimed.

1. A reflection type liquid crystal display device, comprising: asubstrate including a display region, a pad region, and a boundaryregion between the display region and the pad region; a wiring layerformed on the substrate, the wiring layer comprising a first metal layerand a second metal layer stacked on the first metal layer, the wiringlayer having a wiring layer terminal corresponding to the pad region; afirst passivation layer formed on the substrate having the wiring layer,the first passivation layer having a pad contact hole that exposes thefirst metal layer corresponding to the wiring layer terminal and aportion of the wiring layer connected to the wiring layer terminal; apad electrode continuously formed on a sidewall and a bottom of the padcontact hole and on a portion of the first passivation layer, the padelectrode comprising a transparent conductive layer and making contactwith the first metal layer corresponding to the wiring terminal and aportion of the wiring layer connected to the wiring layer terminal; asecond passivation layer formed directly on the pad electrodecorresponding to the boundary region and directly on the firstpassivation layer corresponding to the display region and the boundaryregion; and a reflective electrode formed on the second passivationlayer corresponding to the display region; wherein the pad contact holeextends to a position under the second passivation layer located on theboundary region.
 2. The reflection type liquid crystal display device asclaimed in claim 1, wherein the second metal layer of the wiring layercomprises aluminum (Al) or aluminum alloy.
 3. The reflection type liquidcrystal display device as claimed in claim 1, wherein the pad electrodeis extended along the pad contact hole to the boundary region.
 4. Areflection type liquid crystal display device, comprising: a substrateincluding a display region, a pad region, and a boundary region betweenthe display region and the pad region; a gate wiring formed on thesubstrate, the gate wiring comprising a first metal layer and a secondmetal layer stacked on the first metal layer, the gate wiring having agate line prolonged in a first direction and a gate terminal connectedto an end of the gate line, the gate terminal corresponding to the padregion; a gate insulating layer formed on the substrate having the gatewiring; a data wiring formed on the gate insulating layer, the datawiring having a data line prolonged in a second direction substantiallyperpendicular to the first direction and a data terminal connected to anend of the data line, the data terminal corresponding to the pad region;a first passivation layer formed on the substrate having the data wiringand the gate insulating layer, the first passivation layer having afirst pad contact hole formed through the gate insulating layer toexpose the first metal layer corresponding to the gate terminal and aportion of the gate line connected to the gate terminal; a gate padelectrode continuously formed on a sidewall and a bottom of the firstpad contact hole and on a portion of the first passivation layer, thegate pad electrode comprising a transparent conductive layer and makingcontact with the first metal layer corresponding to the gate terminaland a portion of the gate line connected to the gate terminal; a secondpassivation layer formed directly on the gate pad electrodecorresponding to the boundary region and directly on the firstpassivation layer corresponding to the display region and the boundaryregion; and a reflective electrode formed on the second passivationlayer corresponding to the display region; wherein the first pad contacthole extends to a position under the second passivation layer located onthe boundary region.
 5. The reflection type liquid crystal displaydevice as claimed in claim 4, wherein the second metal layer of the gatewiring comprises aluminum or aluminum alloy.
 6. The reflection typeliquid crystal display device as claimed in claim 4, wherein the gatepad electrode is extended along the first pad contact hole to theboundary region.
 7. The reflection type liquid crystal display device asclaimed in claim 4, further comprising a data pad electrode formed froma same layer as in the gate pad electrode, the data pad electrode makingcontact with the data terminal via a second pad contact hole formedthrough the gate insulating layer and the first passivation layer overthe data terminal.
 8. The reflection type liquid crystal display deviceas claimed in claim 4, wherein the first passivation layer comprises aninorganic material and the second passivation layer comprises an organicmaterial.
 9. The reflection type liquid crystal display device asclaimed in claim 4, wherein the second passivation layer has a contacthole exposing a portion of the data line over the display region. 10.The reflection type liquid crystal display device as claimed in claim 9,wherein the reflective electrode is connected to a portion of the dataline over the display region through the contact hole.
 11. A method ofmanufacturing a reflection type liquid crystal display device, themethod comprising: forming a wiring layer on a substrate including adisplay region, a pad region, and a boundary region between the displayregion and the pad region, the wiring layer comprising a first metallayer and a second metal layer stacked on the first metal layer, thewiring layer having a wiring layer terminal corresponding to the padregion; forming a first passivation layer on the substrate having thewiring layer, the first passivation layer having a pad contact hole thatexposes the first metal layer corresponding to the wiring layer terminaland a portion of the wiring layer connected to the wiring layerterminal; continuously forming a pad electrode comprising a transparentconductive layer on a sidewall and a bottom of the pad contact hole andon a portion of the first passivation layer, the pad electrode makingcontact with the first metal layer corresponding to the wiring terminaland a portion of the wiring layer connected to the wiring layerterminal; forming a second passivation layer directly on the padelectrode corresponding to the boundary region and directly on the firstpassivation layer corresponding to the display region and the boundaryregion; and forming a reflective electrode on the second passivationlayer corresponding to the display region.
 12. The method ofmanufacturing a reflection type liquid crystal display device as claimedin claim 11, wherein the second metal layer of the wiring layercomprises aluminum or aluminum alloy.
 13. The method of manufacturing areflection type liquid crystal display device as claimed in claim 11,wherein the step of forming the first passivation layer comprises:forming the first passivation layer on the substrate having the wiringlayer; partially etching the first passivation layer to form the padcontact hole that exposes the second metal layer corresponding to thegate terminal and a portion of the wiring layer connected to the wiringlayer terminal; and etching the exposed second metal layer to expose theunderlying first metal layer.
 14. The method of manufacturing areflection type liquid crystal display device as claimed in claim 11,wherein the pad electrode is formed so as to be extended along the padcontact hole to the boundary region.
 15. A method of manufacturing areflection type liquid crystal display device, the method comprising:forming a gate wiring on a substrate including a display region, a padregion and a boundary region between the display region and the padregion, the gate wiring comprising a first metal layer and a secondmetal layer stacked on the first metal layer, the gate wiring having agate line prolonged in a first direction and a gate terminal connectedto an end of the gate line, the gate terminal corresponding to the padregion; forming a gate insulating layer on the substrate having the gatewiring; forming a data wiring on the gate insulating layer, the datawiring having a data line prolonged in a second direction substantiallyperpendicular to the first direction and a data terminal connected to anend of the data line, the data terminal corresponding to the pad region;forming a first passivation layer on the substrate having the datawiring and the gate insulating layer, the first passivation layer havinga first pad contact hole formed through the gate insulating layer toexpose the first metal layer corresponding to the gate terminal and aportion of the gate line connected to the gate terminal; continuouslyforming a gate pad electrode comprising a transparent conductive layeron a sidewall and a bottom of the first pad contact hole and on aportion of the first passivation layer, the gate pad electrode makingcontact with the first metal layer corresponding to the gate terminaland a portion of the gate line connected to the gate terminal; forming asecond passivation layer directly on the gate pad electrodecorresponding to the boundary region and directly on the firstpassivation layer corresponding to the display region and the boundaryregion; and forming a reflective electrode on the second passivationlayer corresponding to the display region.
 16. The method ofmanufacturing a reflection type liquid crystal display device as claimedin claim 15, wherein the second metal layer of the gate wiring comprisesaluminum or aluminum alloy.
 17. The method of manufacturing a reflectiontype liquid crystal display device as claimed in claim 15, wherein thestep of forming the first passivation layer comprises: forming the firstpassivation layer on the substrate having the data wiring; partiallyetching the first passivation layer and the gate insulating layer toform the first pad contact hole that exposes the second metal layercorresponding to the gate terminal and a portion of the gate lineconnected to the gate terminal; and etching the exposed second metallayer to expose the underlying first metal layer.
 18. The method ofmanufacturing a reflection type liquid crystal display device as claimedin claim 17, wherein a second pad contact hole exposing the dataterminal is formed simultaneously in the step of forming the first padcontact hole.
 19. The method of manufacturing a reflection type liquidcrystal display device as claimed in claim 18, wherein a data padelectrode connected to the data terminal through the second pad contacthole is formed simultaneously in the step of forming the gate padelectrode.
 20. The method of manufacturing a reflection type liquidcrystal display device as claimed in claim 15, wherein the gate padelectrode is formed so as to be extended along the first pad contacthole to the boundary region.
 21. The method of manufacturing areflection type liquid crystal display device as claimed in claim 15,wherein the first passivation layer comprises an inorganic material andthe second passivation layer comprises an organic material.
 22. Themethod of manufacturing a reflection type liquid crystal display deviceas claimed in claim 15, wherein a contact hole exposing a portion of thedata line in the display region is formed in the step of forming thesecond passivation layer.